1. Field of the Invention
The present invention relates to an improved U-nut which will frictionally mount on a sheet material and engage a bolt hole in the sheet, and which is used in securing an object to a sheet material.
1. Description of the Prior Art
A U-nut currently used in the automotive industry for securing objects to sheet materials comprises a U-nut having two joined legs between which the sheet material is disposed. Typically, one leg has a semi-circular tongue which extends toward the other leg, and which frictionally engages the sheet material and a bolt hole therein, and the second leg has integrally formed thereon a threaded barrel which serves as a nut. The semi-circular tongue has a circular hole through which a threaded bolt can be passed to insert into the threaded barrel of the second leg. This known U-nut is described in U.S. Pat. No. 3,426,818 to Derby for a Yielding Nut Retainer. Another such U-nut or J-nut is described in U.S. Pat. No. 3,229,743 to Derby for a Sheet Metal Nut with Yielding Retainer.
It has been found that the prior art U-nuts suffer several practical drawbacks in that they require a relatively high amount of force to push the U-nut onto sheet materials having a thickness greater than 2 millimeters. For example, a U-nut such as that shown in Darby '818 generally requires a push on force in the range of 16 to 20 pounds for a 4 millimeter thick sheet. In addition the manufacturing step of heat treating the U-nut can lead to variations in the gap between the tongue and the second leg, which will also create wide variations in the amount of force necessary to push such a U-nut onto a sheet material of a particular thickness. Such U-nuts also show a large variation of push on force when used with sheet materials of varying thickness. Finally, it has been found that the prior art U-nut may in some cases be easily dislodged; for instance a very low pull off force, on the order of 0.4 pounds of force, is all that is needed to remove the U-nut which has been mounted on thicker sheets such as a 4 millimeter thick sheet.